用选择信号赋值语句(with-select)和移位操作符来实现3

VHDL实现如下:

LIBRARY IEEE;

USE IEEE.STD_LOGIC_1164.ALL;

ENTIDY Trans38 IS

PORT(

  A:IN STD_LOGIC_VECTOR(2 DOWNTO 0);

  Y:OUT STD_LOGIC_VECTOR(7 DOWNTO 0)

  );

END Trans38;

ARCHITECTURE behav OF trans38 IS

BEGIN

WITH A SELECT

Y<=  "00000000" SLL CONV_INTEGER(A) when "0001",

          "00000000" SLL CONV_INTEGER(A) when "001" ,    --有效输出为高电平

          "00000000" SLL CONV_INTEGER(A) when "010" ,

          "00000000" SLL CONV_INTEGER(A) when "011" ,

          "00000000" SLL CONV_INTEGER(A) when "100" ,

          "00000000" SLL CONV_INTEGER(A) when "101" ,

          "00000000" SLL CONV_INTEGER(A) when "110" ,

          "00000000" SLL CONV_INTEGER(A) when "111" ;

END behav;

注：来自互联网，未经实机测试，谨慎使用；